This invention relates generally to semiconductor wafer processing and more particularly to the optimization of semiconductor sawing using an internal diameter saw.
An internal diameter saw blade is a thin metal annulus having diamond or other abrasive particles bonded to its inner rim to form a cutting edge. The core of a typical saw blade is about 4-5 mils thick and the cutting edge has a thickness of about 10-11 mils. Internal diameter saws are used in semiconductor manufacturing, for example, to cut silicon ingots into wafers. The flatness, depth of damage and edge perfection of a wafer are dependent upon the degree to which the saw blade follows an ideal plane as it traverses the wafer, as well as its freedom from out-of-plane vibration. Lateral vibration increases the kerf loss for each wafer cut, thus decreasing the yield of wafers per ingot. To meet these requirements the saw blade must be kept under a constant, high tension. An improperly tensioned blade will produce bowed or otherwise defective wafers and the useful life of the blade will be diminished, because the blade becomes unstable with respect to deviation under the forces of cutting. Further, the blade becomes free to vibrate with a greater amplitude than a properly tensioned blade.
Methods and apparatus are known in the art for monitoring blade deviation or displacement from a steady-state position as it moves through an ingot. However, these systems do not indicate whether the blade requires retensioning or merely needs dressing. If the blade is dressed when retensioning was the proper course of action, the result will be lower wafer quality and yield. It is known in the art to measure blade tension by applying a force to the blade rim through a force gauge or a balance arm in contact with the blade and then reading deflection with a dial indicator. This method, however, requires stopping of the saw, assembly and calibration of sensitive, precision equipment, and numerous measurements by a skilled operator. This is both expensive and time-consuming.
A system and method for measuring tension while the saw blade is installed and rotating is disclosed in copending application Ser. No. 432,619 filed herewith, entitled "Apparatus and Method For Measuring Saw Blade Flexure," and assigned to the assignee of the present invention. However, retensioning requires stopping the saw and performing an involved tensioning procedure. This is particularly time-consuming in the case of mechanically tensioned saw blades.